Patients with cystic fibrosis (CF) have a high incidence of diabetes mellitus (DM) and glucose intolerance. The impact of CF and DM on the morbidity and mortality of CF is not well understood. The hypothesis of the study is that the degree of insulin resistance will be correlated with negative clinical outcome. Insulin sensitivity in CF patients with and without DM will be measured and compared, along with controls. The degree of insulin sensitivity/resistance will be correlated with clinical outcome. To date, our data have indicated that CF subjects have peripheral insulin resistance which correlates with worsened clinical outcome. They also have increased hepatic glucose production, and increased basal proteolysis when compared to control volunteers. CF subjects also demonstrate resistance to insulin's anabolic effects on proteolysis and hepatic insulin resistance, as well as a tendency toward de novo lipogenesis.